The present invention relates generally to facsimile (fax) transcoding and more particularly to dynamic facsimile transcoding in a unified messaging platform.
Unified messaging is the integration of different streams of communication (e.g., email, voicemail, short message service (SMS), fax, etc.) into a single, unified message store (e.g., a unified messaging platform) accessible from a variety of user devices. In facsimile handling, when a fax call is forwarded to voicemail in a unified messaging platform, if the calling endpoint is a facsimile machine, the fax can be transferred to the unified messaging platform system and later accessed via other communications methods (e.g., email, web portal, etc.).
Generally, there exists two common mechanisms for real-time transport of faxes over Voice over Internet protocol (VOIP) networks—the G.711 ITU-T standard (referred to herein as G.711 fax or simply G.711) and the ITU standard T.38 (referred to herein as T.38 fax or simply T.38).
With G.711 fax, a fax call is treated the same as a voice call. Fax modems communicate directly through the G.711 real-time transport protocol (RTP) stream. Media Gateways are typically still required to disable silence suppression, disable echo cancellation, perform tone detection, and renegotiate the sessions to G.711 if higher compression codecs are in use (e.g., G.729).
There are several drawbacks to using G.711 fax. First, G.711 fax is very susceptible to timing errors in an Internet protocol (IP) network. A lost packet can cause fax modems to lose sync and drop the call. Second, G.711 is bandwidth intensive, using up to twenty times the bandwidth of an equivalent T.38 call. Third, G.711 is expensive to implement in a VOIP platform. G.711 fax requires dedicated digital signal processor (DSP) resources for decoding. A unified messaging platform processing G.711 fax therefore requires dedicated fax servers with DSPs.
In contrast, T.38 fax creates a higher-level protocol that abstracts the fax data from lower layers. T.38 fax is much more robust than G.711, supports reliable transport mechanisms (e.g., transmission control protocol (TCP)), and allows redundant data to be added in a user datagram protocol (UDP) mode. Additionally, T.38 is more tolerant of timing problems or errors in IP networks and utilizes considerably less bandwidth than G.711 fax. Furthermore, since T.38 provides fax data abstraction, it can be implemented on general-purpose media servers without the need for costly DSPs since G.711 decoding and analog T.30 fax processing are not required.
Unfortunately, there are a number of legacy devices still used in VOIP networks that do not support T.38 fax. Session border controllers (SBC) provide transcoding capabilities, but the transcoding policies must be statically configured. That is, a VOIP network connected to the SBC must be designated either as T.38 capable or as T.38 incapable. If designated as T.38 incapable, the SBC will transcode all calls from that network from G.711 to T.38. Transcoding is a complex and costly process that requires extensive DSP resources.
Accordingly, improved systems and methods for facsimile transcoding are required.